Automotive air conditioning systems use a condenser, generally mounted in front of the radiator behind the grill, to dump heat from the system refrigerant after it has been warmed in an evaporator and compressed in a compressor. Older design condensers were generally of the serpentine fashion, having one or two long lengths of flat, extruded tubing wound back and forth in a sinuous pattern, or the tube and fin type, with a series of U-shaped, round tubes, the ends of which fed into manifolds.
A more recently adopted type of condenser is the tank and tube type of condenser, in which a pair of parallel, usually vertically mounted tanks serve as the manifolds at opposite ends of a plurality of relatively short, straight sections of tube. In one type of such condenser, the manifold tanks are basically cylindrical sections of pipe. The ends of the tubes run through slots in the pipes, so the width of the tubes, referred to often as the core width of the condenser, is comparable to the diameter of the pipe shaped tank. In another type of tank and tube condenser, the so called headered tank type, the tank is basically rectangular in cross section. Three of the four walls are generally flat or planar, provided by a channel shaped extrusion, while the fourth wall is provided by a slotted header plate crimped and brazed into the extrusion. The header plate is slotted to receive the ends of the tubes.
There are advantages and disadvantages unique to either design. The rectangular shape is, for equal wall thicknesses, inherently less resistant to bursting under pressure than is the round cross sectioned, cylindrical pipe. However, the rectangular tank is structurally better adapted to provide the manifold function. That is, the capacity of a condenser, its ability to dump heat, is directly related to the width of its tubes, sometimes called the core width. There must be a dimension in the manifold tanks large enough, when slotted, to receive the width of the tube ends. With a cylindrical manifold, it is the diameter of the pipe that must be large enough to accept the tube width, and the volume of the tank will go up with the square of the tube width. This translates into a lot of extra volume and size, volume not really needed for refrigerant capacity. With the rectangular tank, only the header plate (and opposed side wall) of the tank absolutely have to be widened to accept a wider tube. The face walls of the tank can remain the same size, so tank volume, theoretically, need only increase linearly with capacity, not with the square. As a practical matter, however, tank wall thickness will have to increase significantly to give sufficient burst pressure, with a wider tank, increasing tank weight and cost significantly. Of course, a larger tank means that all the components, tube, fin, tank extrusion, header plate, will be of a new and larger size, with obvious increases in tooling costs.